Recent snow may be sitting on a weak layer that may take longer than usual to stabilize. It can be tricky to characterize as it may present differently depending on elevation and aspect. Make sure you gather relevant information before stepping out into more committing terrain.
Storm slabs are most likely to remain reactive at upper elevations where the recent snow has been wind loaded over a weak layer of preserved surface hoar or where it sits over a freezing rain crust below 1500 m.
A weak system will brush down the west coast of the island Thursday night and into Friday. Snowfall amounts will be highest along the western slopes, which could see as much as 20 cm Thursday night and 15 cm over the day on Friday. Lighter snowfall is expected in most areas.
Thursday night: 5-10 cm new snow in most areas. Strong low elevation wind switching southeast and easing. Freezing level 300 m.
Friday: Mostly cloudy, 5-10 cm new snow in most areas. Moderate southeast winds easing. Treeline high temperatures near -6 C, freezing level 500 m.
Saturday: Mainly cloudy, scattered flurries with 2-10 cm of snow. Light to moderate southwest winds. Treeline high temperatures near -8 C. Freezing level dropping to sea level.
Sunday: A mix of sun and cloud. Wind increasing to strong southeast. Treeline temperatures dropping to -15 C.
Observers on Saturday reported roller balls and small wet loose avalanches releasing naturally in saturated snow on steep features below treeline.
On Friday, storm slabs may remain triggerable, particularly where new snow has been transported by wind into deeper drifts over preserved surface hoar or a freezing rain crust at upper elevations.
Light amounts of new snow continue to accumulate 15-30 cm on top of a recent freezing rain crust that extends up to around 1500 m. Our field team reported easy shears on this layer in their MIN report from during the storm on Wednesday.
At upper elevations that did not see rain, a layer of surface hoar may be preserved under the recent snow. You can see photos of the surface hoar prior to the storm in our field team's MIN report from Elk Mountain on Monday. Northwest winds at upper elevations have likely resulted in atypical cross-loading or reverse-loading patterns.
A crust-facet sandwich formed in early December can now be found a meter deep. These layers show limited reactivity and are well bridged by strong snowpack layers above them. Below, the snowpack is generally well-settled.
